The field is fuel injection in opposed-piston engines in which a combustion chamber is defined between end surfaces of pistons disposed in opposition in the bore of a ported cylinder. More particularly, the field includes direct fuel injection through the side of a cylinder into the combustion chamber of an opposed-piston engine.
Fuel injection is an important component of combustion in diesel engines and is one of the processes that affect the efficiency with which the diesel engine operates. It is desirable to manage fuel injection so as to maximize the heat produced by combustion while minimizing transfer of the heat of combustion to engine components such as cylinder bore and piston surfaces. An opposed piston engine typically employs two fuel injectors that inject fuel in opposing directions along a diameter of the cylinder. See, for example, the fuel injection constructions described and illustrated in commonly-owned US publication 2012/0073541 A1.
A diesel injector typically includes a nozzle with a plurality of holes through which fuel is injected. The holes are arranged radially with respect to an axis of the injector. Injection through multiple holes produces a spray pattern constituted of one or more plumes that project radially outward from the injector axis. Typically a plume is represented by a vector that forms an angle (a “spray angle”) in a respective plane shared with the injector axis. A wider spray angle results in a plume being injected at a higher angle away from the injector axis. This is desirable because the fuel of each individual plume burns in the presence of air independently of the other plumes. There is less interaction of individual plumes and hence, a faster burn time. However, in an opposed piston engine, a wider spray angle also pushes the plume and hence the flame closer to the cylinder bore and piston surfaces, resulting in combustion near those surfaces. This can result in excessive heat transfer into the cylinder liner and piston walls. Such heat transfer results in a loss of power; and a higher heat transfer loss means lower indicated thermal efficiency of the engine. Heat transfer can be reduced by directing the plumes away from the cylinder bore surface.
To reduce the heat transfer across the pistons and walls, the spray angle of the multiple holes is reduced. However, this leads to interaction of opposing spray plumes that concentrates fuel-vapor, entrained air, and some hot combustion products around the central region of the combustion chamber. This inhibits air/fuel mixing, which results in increasing burn time.
To achieve both faster burn and reduced heat transfer to the cylinder bore and piston surfaces in opposed piston operation, it is desirable that fuel injection spray patterns minimize interaction of sprays (both from the same injector and opposite injectors), minimize the transfer of heat to the piston and cylinder bore surfaces, and encourage faster fuel/air mixing.